The researchers said the current ABC system was too arbitrary, and failed to give specific information about the relative risks of each drug.

It also gave too much importance to unusual reactions, which would only affect a tiny number of users.

Professor Nutt said people were not deterred by scare messages, which simply served to undermine trust in warnings about the danger of drugs.

He said: "The current system is not fit for purpose. Let's treat people as adults. We should have a much more considered debate how we deal with dangerous drugs."

He highlighted the fact that one person a week in the UK dies from alcohol poisoning, while less than 10 deaths a year are linked to ecstasy use.

Professor Blakemore said it was clear that current drugs' policies were not working.

"We face a huge problem. Illegal substances have never been more easily available, or more widely abused."

He said the beauty of the new system, unlike the current version, was that it could easily be updated to reflect new research.

Professor Leslie Iversen, a member of the Academy of Medical Sciences group considering drug policy, said the new system was a "landmark paper".

He said: "It is a real step towards evidence-based classification of drugs."

Professor Iversen said the fact that 500,000 young people routinely took ecstasy every weekend proved that current drug policy was in need of reform.

Home Office Minister Vernon Coaker said: "We have no intention of reviewing the drug classification system.

"Our priority is harm reduction and to achieve this we focus on enforcement, education and treatment."

He said there had been "unparalleled investment" of £7.5 billion since 1998, which had contributed to a 21% reduction in overall drug misuse in the last nine years and a fall of 20% in drug related crime since 2004.

But he added: "The government is not complacent and will continue to work with all of our partners to build on this progress."